Integrated circuits (ICs) are generally fabricated in an array on or in a semiconductor substrate. ICs generally include several layers formed over the substrate. One or more of the layers may be removed along scribing lanes or streets using a mechanical saw or a laser. After scribing, the substrate may be throughcut, sometimes called diced, using a saw or laser to separate the circuit components from one another.
Laser processing systems employed for processing dynamic random access memory (DRAM) and other devices commonly use a Q-switched diode pumped solid state laser. When processing memory devices for memory repair applications, for example, a single laser pulse is commonly employed to sever an electrically conductive link structure. In another industrial application, Q-switched diode pumped solid state lasers are used to trim resistance values of discrete and embedded components.
Some laser processing systems use different operating modes to perform different functions. For example, the ESI Model 9830 available from Electro Scientific Industries, Inc. of Portland, Oreg., the assignee of the present patent application, uses a diode pumped Q-switched neodymium-doped yttrium vandate (Nd:YVO4) laser operating at a pulse repetition frequency of approximately 50 kHz for laser processing of semiconductor memory and related devices. This laser system provides a pulsed laser output for processing link structures and a continuous wave (CW) laser output for scanning beam-to-work targets. As another example, the ESI Model 9835, also available from Electro Scientific Industries, Inc., uses a diode pumped Q-switched, frequency-tripled Nd:YVO4 laser for laser processing semiconductor memory and related devices. This laser system uses a first pulsed laser output at a PRF of approximately 50 kHz for processing link structures and a second pulsed laser output at a PRF of approximately 90 kHz for scanning beam-to-work targets. In some systems, higher PRFs (e.g., approximately 100 kHz) are also possible. Generally, the pulse widths of laser pulses generated by such laser systems are functionally dependent on the PRF selected and are not independently adjustable based on differences between target structures or other process variables.
FIGS. 1A and 1B are example temporal pulse shapes of laser pulses generated by typical solid state lasers. The pulse shown in FIG. 1A may have been shaped by optical elements as is known in the art to produce a square-wave pulse. As shown in FIGS. 1A and 1B, a typical solid state pulse shape is well described by its peak power, pulse energy (time integration of the power curve), and pulse width measured at a full-width half-maximum (FWHM) value. Signals from a pulse detector may be used to determine pulse energy and/or peak power. The pulse detector may include a diode coupled to an analog peak capture-and-hold circuit for peak power sensing. The pulse detector may also include an analog integration circuit for pulse energy measurements.
One problem for laser processing is that the results tend to be highly material dependent. For example, one laser type (or set of laser parameters) may be ideal for cutting metals, while a different laser type (or set of laser parameters) may be ideal for cutting glass.
One example of a challenging problem is the singulation of semiconductor devices mounted on die attach film (DAF). This problem is generally addressed in production by using mechanical diamond saws with ultra-thin blades because laser dicing with known processes tend to produce a die with lower mechanical strength compared to that produced by mechanical sawing. Incorporation of fragile low-k dielectric materials into these semiconductor devices along with reduction of the silicon wafer thickness has increased the difficulty for mechanical saw dicing, leading to slower throughputs and more yield losses. Previously attempted solutions include using lasers to scribe the low-k semiconductor layers prior to mechanical saw dicing, combining laser dicing with a post-etch process to strengthen the die, or using a full-cut laser dicing system with two lasers having different pulse widths.
Unlike full-cut laser dicing, laser scribing of copper and/or low-k dielectric devices has generally been adopted by manufacturing. However, increases in scribing throughput are still desired.